Colored cellulosic film



Patented Jan. 19, 1943 2.308.732 COLORED cELpULosrc FILM William D. White, Kenmore, N. Y., assignor to E. I. du Pont vlie Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing.

Application April 20, 1940, Serial No. 330,731

20 Claims. 3]. 117-144) other surfaces when subjected to pressure for considerable periods of time.

Transparent, non-fibrous pellicles, such as those regenerated from viscose and related cellulosic solutions or dispersions, and intended for use as wrapping material, are generally impregnated with glycerol or the like in order to impart thereto sufllcient flexibility, toughness and durability to make them suitable for this purpose. Unfortunately the addition of such substances induces a certain inherent stickiness or tackiness which causes layers of the impregnated material to adhere together rather firmly when subjected to pressure for periods of several days or more. Stacks of sheets of such materials have been found to adhere with such tenacity that they cannot be readily separated for use. It has also been found that a similar disadvantage occurs in rolls of the material which have been stored for several days. They unroll with difliculty (due to adhesion of the film surfaces), and for this reason are unsatisfactory for operation upon automatic wrapping machinery, etc. Furthermore, sheet material of such a character adheres to the surfaces encountered in automatic machinery, and will not pass through such machinery with the facility requisite for smooth operation.

It has been suggested that this disadvantage of tackiness could be overcome by applying small amounts of suitable substances, which will render the webs non-tacky, to their surfaces. A number of such materials, commonly called sizes, have been proposed. Recently an alkaline sizing composition based on sodium silicate (U. S. A. Patent No. 2,206,046 issued Nov. 9, 1939, to Pollard), which maintains the webs in transparent, hazefree, and otherwise satisfactory condition even upon the application of pressure for considerable periods of time, has been developed.

Preferably this caustic alkaline material size is applied to the gel web and the web subsequently dried upon conventional apparatus.

It has been observed that these sodium silicate sizes adversely affect the color produced in dyed film, particularly film dyed with alkaline sensitive dyes. Generally such film is dyed in the original gel condition and washed before it is softened and sized. The aforementioned sizes. based on sodium silicate, are such a great improvement in the art, and have so many advantages that their employment with colored films is highly desirable. I

This invention had for an object the production of attractively colored regenerated cellulose type pellicles which were transparent, flexible, durable and free from any inherent tackiness. A more specific object was to prevent the detrimental effect of alkaline sizing baths, such as those based on alkali metal silicates, upon nonfibrous sheet material dyed with alkali sensitive dyes such as Pontamine Sky Blue 6 BX (C. I. 518). Still further objects were to improve the color in sized regenerated cellulose film dyed with azo dyes, particularly disazo dyes. A general advance in the art, and other objects which will appear hereinafter, are also contemplated.

It has now been found that the incorporation of the ammonium salt of a polycarboxy organic acid, which does not affect the alkalinity of the treating solution (preferably one which is neutral to litmus), in the sodium silicate sizing bath results in the production of sized film which is satisfactorily colored. In general the objects of this invention are accomplished by treating a gel regenerated cellulose or like web prepared in the conventional manner with an alkaline sensitive dye, and thereafter softening and sizing the dyed web with a water-miscible softening agent, an emulsified alkaline sizing material, and material consisting of ammonium hydrogen salt of polybasic acid, and subsequently drying said web.

From the following description and specific examples, in which are disclosed certain embodiments of the invention as well as details of what is believed to be the best mode for carrying out the invention, it will be apparent how the foregoing objects and related ends are accomplished. The parts are given by weight throughout the application.

Example I A gel web of regenerated cellulose (containing approximately 350% water, based on the cellulose), prepared according to the method described in U. S. A. Patent No. 1,548,864, was, after regeneration, desulfuring and washing, passed through an aqueous bath containing 0.25% of the blue dye Pontamine Sky Blue 6-BX (C. I. 518) and then through a tank of clear wash water. The web was then sized by passing through an aqueous bath of the following composition:

Per cent Glycerol 4.5 Stearamide 0.14 sodium silicate 0.14 Stearic acid 0.16 Ammonium acid tartrate 0.07 Water "a 94.99

The film was then passed between rubber surfaced squeeze rolls, which removed excess liquid from the surfaces, and then subjected to a drying operation in the conventional manner. After drying, the film contained 16% glycerol, and was found to have a pH of 6.2. The color was a very satisfactory shade of blue.

A film prepared according to this same method but with the exception that the acid ammonium tartrate was omitted from the impregnating bath, was found to have, after drying, an unsatisfactory brownish cast.

Example II The procedure of Example I was repeated, using gel web dyed with Constellation Blue PBS (C. I. 520) and a size bath consisting of:

Per cent Glycerol 5.0 Stearamide 0.08 Palmitamide 0.07 Sodium silicate 0.14 Stearic acid 0.16 Ammonium acid succinate 0.09

Water 94.46

The film was dried at a temperature of 60-80 C. The results were comparable.

Example III Glycerol 4.1 Stearamide; 0.14 Sodium silicate 0.14 Stearic acid 0.16 Ammonium acid citrate 0.05 Water 95.41

The excess liquid was removed from the surface of the film, and the resulting web dried as before. The dried product was found to have a pH of 6.8 and a satisfactory green color.

In the absence of the ammonium acid citrate in the size bath, a film produced in the corresponding manner had a green color with a brownish or reddish cast and was dull.

Example IV The procedure of Example I was repeated,

using gel web dyed with Nebula Blue 2-PS (C. I. v

406) and a size bath consisting of Per cent Glycerol 5.2 Stearamide 0.14 Sodium silicate 0.15 Palmitic acid ,-a 0.04 Myristic acid 0.04 Stearic acid 0.10 Ammonium acid malate 0.05

Water 94.28

The presence of the ammonium acid malate overcame a dull discoloration in the film.

Example V The preparation of the following specific softener-size bath will further illustrate the in vention. Stearic acid (1.3 parts) and stearamide 1.1 parts) were melted, added to 56 parts of water, and thoroughly mixed. Sodium silicate solution (2 parts) comprising 28% S102, 8.5% Nazo and 63.5% H2O were then added with stirring. The concentrated dispersion thus formed, at a temperature of -90 C., was added with stirring to an aqueous bath containing 7.5% glycerin and 0.05% diammonium phosphate to form a 0.4% colloidal dispersion of total solids. This bath was then used in the usual manner for softening and sizing dyed continuous webs of regenerated cellulose. Similar results were obtained by replacing the diammonium phosphate in the bath with the same quantity of ammonium acid citrate.

The greatest improvement has been noted in the case of the blue and green dyes, particularly those which are changed in color by alkaline conditions. to materials dyed with the specific dyes of the examples, but is applicable to material dyed with other dyes of this character, such as those produced according to U. S. A. Patent No. 421,640.

While the invention is mainly applicable to regenerated cellulose film prepared from viscose or by the cuprammonium process, it is also applicable to web prepared from lowly substituted cellulose ethers and cellulose esters which'are dispersible in alkaline aqueous media, for examp-le, products of U. S. A. Patent No. 2,123,883 (Ellsworth) Any of, the well known softening agents may be employed for softening the film. The com- Other materials of this character which may be specifically mentioned are those of the examples and ammonium acid carbonate, ammonium acid sulfate, ammonium acid malonate, and ammonium acid maleate. The salts must contain a plurality of carboxyl residues (groups, nuclei, radicals), and one or more may be used in the same bath.

The sizing and softening action may, with appropriate precautions, take place in separate baths. In cases where the size and/or softener is applied as an emulsion, the conditions in the sizing bath should be satisfactory for maintaining a stable emulsion. It is immaterial that the conditions for the stable emulsion exist after the film has entered the drier.

In the interest of brevity reference is made to the aforementioned Pollard patent for further details and advantages of the sizing baths utilized according to this invention. In. addition to the advantages recited in the Pollard patent, the present invention provides for good color, particularly in blue and green film. As a result of the addition of acid ammonium salts of polybasic acids to alkaline sizing baths as described above, highly transparent, flexible, durable, nonsticking film of a clear true color is obtained.

The invention is not limited asoavss As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. The process of improving the color in dyed regenerated cellulose film which comprises treating gel regenerated cellulose film dyed with a dye whose color is deleteriously affected by drying under alkaline conditions with an alkaline size bath containing an acid ammonium polybasic acid salt and drying the resultant film.

2. The process of claim 1 when the size bath contains a softener.

3. The process of claim 1 when an acid ammonium salt of a polybasic organic acid is em- 6. The process 01' claim 1 when the size bath consists 0!:

Per cent Glycerol 4.1 Stearamide 0.14 Sodium silicate 0.14

Stearic acid 0.16

Ammonium acid citrate 0.05 Water 95.41

7. The process of claim 1 when the dye is Tahoe Green G, the softener is glycerol, the size base is sodium silicate and the salt is ammonium acid citrate.

8. The process which comprises dyeing gel regenerated cellulose sheet with an azo dye which is discolored upon drying under alkaline conditions, treating the dyed sheet with an alkaline size solution containing an acid ammonium polybasic acid salt, and drying the sized sheet.

9. The process which comprises dyeing gel regenerated cellulose sheet with an azo dye from the group consisting of Tahoe Green G and Pontamine Sky Blue G-BX, treating the dyed sheet with an alkaline size solution containing an.

passing the sized web through a size bath consisting of:

and drying the resultant sized web.

13. The process which comprises dyeing gel regenerated cellulose film with a dye wh'ose.

shade is deleteriously afiected by drying under alkaline conditions, treating said dyed film with an alkaline size bath containing an acid ammonium polybasic acid salt, and drying the resultant film.

14. The process which comprises passing gel regenerated cellulose film dyed with a dye whose true color is not obtained when the film is dried under alkaline conditions, through a size bath containing an acid ammonium polybasic acid salt, and drying the resultant sized film.

15. The process of claim 14 when the dye is an azo dye.

16. The process of claim 14 when the dye is a member oi the group consisting of Tahoe Green G and Pontamine Sky Blue B-BX.

17. The process of claim 14 when the size bath consists oi: V

Per cent Glycerol 4.1 Stearamide 0.14 Sodium silica 0.14 Stearic acid 0.16 Ammonium acid citrate 0.05 Water 95.41

l8. The process of claim 14 when the dye is Tahoe Green G and the ammonium salt is ammonium acid citrate. v

19. The process of claim 14 when the dye is Tahoe Green G, the ammonium salt is ammonium acid citrate and the size bath contains sodium silicate.

I 20. The process of claim 14 when the size bath consists of:

Per cent Glycerol 4.5 Stearamide 0.14 Sodium silica 0.14 Stearic acid 0.16 Ammonium acid tartrate 0.0! Water 94.99

WILLIAMID. WHITE. 

